Just had the cover off my BDB today, and I can verify that it would be easy as pie to rig it so that micro switch on the water dispenser handle remains open, so that the brew pump doesn't shut off when you are trying to vent pressure down during the extraction.

I am one who has been experimenting with lower extraction pressure on my pump machines (I'm also a lever head), and while fiddling with backing off the spring pressure in the BDB's OPV, I came to the conclusion that you don't want to take it down much less than 7bar via OPV adjustment as the screw will be out far enough to possibly leak. I was looking at the possibility of finding a lighter spring. Turns out I was barking up the wrong tree. I was failing to recognize the easy solution that this tech tour-de force already had up its sleeve: the ability to set pump pressure via software. You can set your pre infusion pump pressure to anywhere between 55% and 99% of max, and then If you set your pre infusion duration to 99 seconds, you can cover your entire extraction time and then some. I extract by weight, so I cut the pump when the scale under the demitasse reads target mass. After I rig the water dispenser micro switch, I'll be able to play with pressure profiles... But one step at a time. For now I'm just trying to get comfortable with extracting a simple linear but lower than traditional pressure before I start adding more variables.

-Peter

...split from Breville BES920XL "The Dual Boiler" - My Experience by moderator...

Exactly. AFTER I set my OPV to 7 (down from 10), I realized (actually it was pointed out to me) that adjusting the OPV was unnecessary. But, with 100% pressure at 7 bar, I can dial in a range of lower pressures with no difficulty (though, I haven't gone low enough to justify removing the cover ).

The software solution does eliminate the stepped pressure increase from preinfusion to full infusion pressure, but your micro switch will help solve that problem. Please post your micro switch mod, complete with pics and parts, when you make the move!

You can set your pre infusion pump pressure to anywhere between 55% and 99% of max

Does this actually measure and control pressure or is it something like pump power or duty cycle?

pcrussell50 wrote: You can set your pre infusion pump pressure to anywhere between 55% and 99% of max, and then If you set your pre infusion duration to 99 seconds, you can cover your entire extraction time and then some. I extract by weight, so I cut the pump when the scale under the demitasse reads target mass. After I rig the water dispenser micro switch, I'll be able to play with pressure profiles... But one step at a time. For now I'm just trying to get comfortable with extracting a simple linear but lower than traditional pressure before I start adding more variables.

Using the preinfusion pressure setting with 99 seconds preset time is a brilliant idea. Right away I can set to brew the shot at 7 or 8 bar, and use my existing 2 bar play from the water tap to get down to a lower start and finish pressure, a ramp up and ramp down profile. I will try this tomorrow.

Look forward to see how you can rig the switch, I was wondering how that could be done.

jonr wrote:Does this actually measure and control pressure or is it something like pump power or duty cycle?

It is a percentage of the vibe pump's power, but you can set it and then watch the pressure gauge during a shot to then go back and tweak the PI pump power % to adjust it to hit the pressure you want.

jonr wrote:Does this actually measure and control pressure or is it something like pump power or duty cycle?

Varying the pressure output of a vibe pump has been a challenge over the years that has was never satisfactorily solved. HB-ers have played with using dimmer switches to reduce voltage, with generally unsatisfactory results, though there are adherents out there. I might even try it myself on a different vibe pump machine I have. HOWEVER, Breville figured something out with the BDB, that they patented. Bill Crossland (father of the GS/3 and seller of the Crossland CC1), can explain it better than I can.

But in answer to your question, I'm not sure. I doubt it measures pressure. Therefore, I doubt that it is feedback loop controlled, with respect to pressure: IOW, if it senses a pressure drop, it manipulates the pump output upward to maintain a steady pressure. I've only pulled less than a dozen shots so far by remaining in pre infusion and setting the extraction pressure for the pull by setting pre infusion pressure.

Because of the high avoidance factor of this machine by expert baristas and expert technogeeks, there is a LOT we don't fully understand about this super-tech'y machine and its hidden capabilities. I have a fantasy that a technogeek barista will either reverse engineer Breville's source code or adapt an open-source controller to the BDB's sensor and actuator suite. But it's been out long enough, and nobody has taken much interest, so I'm not holding my breath.

-Peter

I have been running my BDB at lower pressures (5-6 bar), using the pre-infusion settings. By setting the duration at 60 sec. and the PP at 68% the pressure slowly builds to 6 bar, then gradually decreases to around 5 at the end of the shot. The flow rate is lower than at full power so the shot usually takes about 40 sec.

Since this thread is about pressure control options on the BDB, I'm reposting here, from another thread where this is embedded and might be hard to find:

[SOLVED] Full continuously variable pressure control via the hot water knob, WITHOUT the pump cutting out:

Ok, I have my BDB apart right now to change some of the old o-rings for the sensors and tubes on the tops of the boilers. While in there, I took note of the microswitch on the hot water knob. The one that turns OFF the brew pump if you turn it too far when trying to pressure profile. Turns out it's SUPER easy to simply remove the microswitch from the housing that holds it against the water knob. You don't have to cut any wires. Just remove it from it's mount and push it out of the way so the switch never gets closed by the knob. You can put it right back any time you want without cutting or splicing. This is good news. Very good news.

Here you can see the switch, sitting in it's mount with the two loose screws. I had taken it out, then put it back for the picture, so I could post it here for your edification:


This is the microswitch, sitting in the mount after removing the two screws and lifting out the whole assembly. Note the brand. Zippy is Italian. As are the Ulka pumps.


This is the switch alone, after snapping it out of the mount, and putting the mount back. You can leave it dangling, or tie it up out of the way, wherever you like.


This easy peasy mod should allow you to open the hot water tap as much as you want, while "pressure profiling" your extraction.

And now?
Tested now with microswitch moved out of the way. Big success. Full pressure control, very linear and easy. You can move the water knob as much as you like without shutting off the brew pump. Very happy with this. No cut wires, no splicing in a dimmer switch with unknown side-effects on the pump control logic. And it does not disable the hot water tap service if you like to use it, though.


Set any steady pump output you want

Alternately, you can set the pump output in the "software", which is very useful for experimenting with low pressure extraction, without having to loosen the OPV, possibly too much, and causing leaks. You do this by using pre-infusion for the whole extraction. Go into the pre-infusion menu and you can set pump output to anywhere from 55% to 95%, and set the time up to 90 seconds, which is more than you need to pull a shot. You can use this to "two stage" profile by starting the extraction at some low pump output of your choice that you set in the software, then switch to full, OPV-limited pump output at any point in the extraction you like. This would be an increasing profile though, and I'm not sure when this would be considered useful. It would be more interesting to have a decreasing profile, but I don't know how to do it in the software as is. I only know how to do this, by manipulating the hot water knob.

The real holy grail this machine is hiding is the brilliant, native control the software has over pump output... That they keep locked away from us. I keep holding out hope that some smart techie of the ilk of a Bill Crossland will obtain full control of the software, so we can program our own pump output profiles.

-Peter